Pass value through if it's not a DateTime.

This solves a crash when a ListBox with a DateTimeField as editable field is
used to filter with a non-date expression (ex: ">01/04/2011").
Still, keep existing exception about None being converted to empty string.


git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@45720 20353a03-c40f-0410-a6d1-a30d3c3de9de

product/Formulator/Widget.py

@@ -1485,8 +1485,10 @@ class DateTimeWidget(Widget):
     # Is it still usefull to test the None value,
     # as DateTimeField should be considerer as the other field
     # and get an empty string as default value?
-    if value in (None, ''):
-      return ''
+    if not isinstance(value, DateTime):
+      if value is None:
+        value = ''
+      return value
 
     use_ampm = field.get_value('ampm_time_style')
     use_timezone = field.get_value('timezone_style')